In a wireless communication system, recently, a service frequency band is gradually raised and a cell radius is gradually reduced in order to smoothly support high speed data communication and accommodate greater traffic, so the operation of an existing centralized cellular wireless network scheme involves much problem. Namely, in the related art method in which the location of a base station (BS) is fixed, flexibility of configuration of a radio link deteriorates, failing to provide an effective communication service in a wireless environment in which a traffic distribution or traffic demand (or call volume) are severely changed.
Thus, a next-generation communication system is required to be distributedly controlled and established and actively cope with a change in an environment such as an addition of a new base station. In order to solve such a problem, a multi-hop relay has been proposed. A multi-hop relay system has advantages in that it can expand a cell service area by covering a local shadow area generated in the cell area, increase a system capacity, and reduce a burden of initial installation costs by using a relay (or a relay station) in an initial situation requiring a small amount of service demand.
FIG. 1 is a view showing a general multi-hop cellular system.
In the multi-hop cellular system, when a mobile station (MS) is distant from a BS or a signal transmission is not smooth due to an obstacle such as a building, or the like, a signal of the MS is relayed to the BS through a relay station (RS), thus increasing cell coverage and resolving a shadow area. As illustrated, when a relay network is configured with two-hop link between a BS 101 and MSs 133, 135, 137, and 139, signals of the MSs are primarily transferred to an RS 121 through the link between the MSs 133, 135, 137, and 139 and the RS 121 and then the RS 121 receives packet data from the plurality of MSs and secondarily relays the signals 141, 143, 145, and 147 received from the MSs to the BS 101 through the link between the RS 121 and the BS 101.
When the RS 121 is used as shown in FIG. 1, resources should be shared to be used by the MSs 133, 135, 137, and 139 and the RS 121 and by the RS 121 and the RBS 101, in comparison to an existing data transmission and reception through a direct link between the BS 101 and the MS 131. Also, when a plurality of RSs 121 and 123 exist, since resources must be shared by RSs, the use of resource is more limited. Thus, in the system using the RS 121, the process of allocating resource and requesting resource are considerably complicated and much signaling overhead is required in comparison to the system using the direct link between the BS 101 and the MS 131. Thus, when the RS 121 is to process the packets 141, 143, 145, and 147 of the plurality of MSs 133, 135, 137, and 139, resource efficiency is degraded and delay is lengthened. In order to solve this problem, a method of integrating the packet data 141, 143, 145, and 147 received by the RS 121 from the MSs 133, 135, 137, and 139 and transferring the same to the BS 101 may be considered.
However, as illustrated, when the RS 121 receives the various packets 141, 143, 145, and 147 from the plurality of MSs 133, 135, 137, and 139 belonging to its area and relays them to the BS 101, the plurality of MSs 133, 135, 137, and 139 use various services such as VoIP 141, data streaming 143, a messenger 145, a file transfer protocol (FTP) 147, Web searching, a video conference service, and the like, as well as simple voice communication, so the packets 141, 143, 145, and 147 transmitted by the MSs 133, 135, 137, and 139 may require various QoS (Quality of Services) according to service types. Thus, if the RS 121 simply integrates the packets received from the MSs and relays them to the BS 101, QoS requirements with respect to various services within the integrated packet could not be met, and when there occurs a frame transmission error of the integrated packet, a data retransmission technique such as a hybrid automatic retransmission request (HARQ) for retransmitting the frame having an error cannot be positively utilized.
FIG. 2 shows a scheme in which the RS 121, which has received various packets 141, 143, 145, and 147 from the plurality of MSs 133, 135, 137, and 139, individually relays the corresponding packets 201, 203, 205, and 207 accumulated in its queue 200 without an integration procedure. As illustrated, the RS 121 accumulates the packets received from the MSs in its queue 200 and individually transfers the packets 201, 203, 205, and 207 to the BS 101 in consideration of a transmission time interval (TTI). In order for the RS to transmit the packets to the BS, a process of requesting resource by the RS from the BS and receiving allocated resource is required, and in this case, the RS should inform the BS about a modulation and coding scheme (MCS) level of transmitted data, address information of the data, an ID of the RS itself (RSID), and the like, through a signaling procedure. However, as shown in FIG. 2, when the packets 201, 203, 205, and 207 to be transmitted to the BS are individually transmitted, resources must be allocated separately over all of the packets, and modulation and coding are performed on each of the packets, increasing complexity in the packet processing and generating signaling overhead and delay.
IEEE 802.16j standard proposes two types of multi-access scheme, i.e., a scheduling scheme and a dedicated channel allocation scheme, with respect to an RS-BS link.
The scheduling scheme is channel-adaptively operated, allowing resources to be effectively used, but overhead and delay may increase due to the resource requesting and allocation process. In addition, according to the scheduling scheme, the MS must perform a resource requesting and allocation process before transmitting data to uplink, i.e., the BS, an access delay and signaling overhead are increased. Also, when the existing scheduling scheme is applied to the RS-BS link as well as to the MS-RS link, the resource requesting and allocation process are inevitably repeatedly performed by the RS and the BS, aggravating the access delay and signaling overhead. Also, in a centralized scheduling scheme and a distributed scheduling scheme for reducing latency, among the scheduling schemes, an aggregation of individual traffic is not considered in the RS, so a resource allocation and data transmission to the BS with respect to a request of the MS is individually made. Such an individual transmission is not efficient compared with the aggregation transmission by the RS, increasing signaling overhead.
Also, as for traffic at the RS, since traffics of MSs belonging to each RS are aggregated, the amount of traffic is large compared with the MSs and a variation is relatively small. However, the existing scheduling scheme does not reflect the characteristics of the RS-BS channels, and although the variation in the amount of traffic and channels of the RS-BS link is small, the RS and the BS simply repeatedly perform scheduling, the signaling overhead and access delay increase as mentioned above.
Meanwhile, in the dedicated channel allocation scheme, data can be immediately transmitted by using exclusively allocated resource without additional signaling, reducing overhead and delay, but since the dedicated channel allocation scheme cannot be adoptively operated for each channel, it is ineffective in using resources. Also, like the scheduling scheme, resource allocation is not made based on the entire RSs included in the BS but resource is allocated according to a corresponding request from an individual RS, and since the real-time and non-real time traffic characteristics are not considered, resource is ineffectively used.